The invention concerns an oil supply system for an automatic transmission of a motor vehicle with one hydrodynamic starting device.
It is known that automatic transmission in motor vehicles use oil for the hydrodynamic transmission of force and power, hydrostatic transmission of force and power, for information processing, for modulation of friction values, lubrication, heat emission and power consumption. As oil supply system serves here an oil circuit which, as a rule, is comprised of an oil sump, an oil filter, an oil pump, control valves, actuators of servoelements, seals, an oil cooler and connecting lines. Via the oil circuit oil volume is passed as pressure medium to shifting elements or for adjustment of variator disks of a variator in CVT transmission, to a converter unit consisting of a hydrodynamic torque converter and a converter lock-up clutch and to a lubrication device by means of which are lubricated or cooled, for example, the bearings of the many shafts, hollow shafts and webs of the planetary sets and servo-organs.
In the automatic transmissions known from the practice, the oil circuit is divided by a main pressure valve in a prioritized primary circuit and a secondary circuit. In a CVT transmission, the primary circuit contains here the pressure supply of the variator disks and shifting elements; in a multi-step transmission usually only the pressure supply of the shifting elements. The pressure of the primary circuit is determined by the main pressure valve, the consumers of the primary circuit being mutually equalized. Compared to the consumers of the primary circuit, the consumers of the secondary circuit have a lower priority in the provision of pressure.
On the primary side of the main pressure valve, when there is an excess of oil volume, the excess oil is sprayed off to the secondary circuit. The secondary circuit usually contains, together with the supply of the lubrication and the pressure supply of the torque converter, the pressure supply of the converter lock-up clutch when the torque converter is attached with its lock-up clutch to the oil supply in the two-line technique. In the known automatic transmissions, the pressure of the secondary circuit is determined by a converter safety valve designed as pressure-limiting valve. The consumers of the secondary circuit are mutually equalized to a pressure level above the predetermined lubrication pressure which is usually adjusted by a separate pressure-limiting valve. In such an arrangement, the main pressure cannot be below the maximum pressure level of the secondary circuit.
The pressure level of the secondary circuit is determined by the required pressure of the converter lock-up clutch when maximum torque is to be transmitted. It is disadvantageous here that in certain operating ranges the minimum main pressure in the primary circuit is determined by the pressure level of the secondary circuit even though for pressure supply of the consumers in the primary circuit a lower pressure level would suffice, for example, in case of small load or open drive train. Deterioration in effectiveness and consumption disadvantages accordingly result.
Although, as a rule, there is an oil oversupply of the primary circuit in operating situations needing a large oil volume in the primary circuit, such as in the case of large adjustment gradients of the variator in a CVT transmission, a brief undersupply in oil volume of the secondary circuit can occur so that the pressure level required does not build up in the secondary circuit. In the case of such an undersupply of the secondary circuit, the pressure in the converter lock-up clutch can drop to lubrication pressure which entails a slipping of the converter lock-up clutch. Due to the high rotation of the primary mover, a loss of comfort also results together with an undesirable wear of the converter lock-up clutch.
Together with the provision of a sufficient oil volume flow for building up a required pressure, the oil supply system in the automatic transmission also has the important function of taking care that the oil in the transmission is cooled in order to be able to remove as heat the power loss generating in the transmission. For this purpose, an oil-cooling device is, as a rule, situated before the lubrication in the secondary circuit wherefore the transmission elements are usually cooled via the supply of lubrication oil. The converter unit is conveniently disposed before the lubrication, since it needs a higher pressure level than the lubrication. To prevent an overpressure in the converter unit, the converter safety valve usually has an oil spray-off edge for discharging excessive oil volume in the oil sump. Consequently, the excessive oil is not cooled which results in a corresponding increase of temperature in the oil sump.
Therefore, the problem on which this invention is based is to make an oil supply system available for an automatic transmission of a motor vehicle, having one oil circuit divided by a main pressure valve into one primary circuit and one secondary circuit with which system can be effectively implemented by adjustment of the lowest possible main pressure, the pressure supply of a converter unit being always ensured. In addition, the oil supply system must make an effective cooling of the circulating oil possible.
According to the invention this problem is solved by an oil supply system.
Therefore, according to the invention, it is proposed to supply the converter lock-up clutch in the operating situations in which it is to be brought to a closing or slipping state with oil, via the primary circuit, with a required minimum pressure while oil is fed to the lubrication device, via the secondary circuit. Otherwise, the converter unit is bound to the secondary circuit.
In a especially advantageous manner, the pressure to be adjusted for the converter unit during the supply through the secondary circuit can be reduced to the cavitation limit of the converter. The inventive tying of the converter lock-up clutch to the primary circuit makes an optimum pressure design on the secondary circuit in the operating states possible with open converter lock-up clutch.
The converter unit is, therefore, always conveniently suppled with enough oil volume while the main pressure in the primary circuit can be below the pressure needed for the closing of the converter clutch, for example, in case of small load. An improved degree of efficiency can be conveniently implemented and thus an economy in fuel.
At the same time, the inventive oil supply system can be used both in multi-step automatic transmissions and in CVT transmission. The inventive oil supply system can, likewise, be used for any hydrodynamic starting elements in combination with an appertaining lock-up clutch, such as a torque converter with integrated lock-up clutch.
For the effective cooling of the oil circulating in the transmission, it is proposed to situate the inventive oil supply system in the secondary circuit in flow direction behind the main pressure valve and before the converter unit, before the lubrication device and before an oil spray-off device for discharging excess of oil volume in the secondary circuit. The cooling of the whole system is hereby improved in the sense that the oil already sprayed off in the oil sump during the pressure adjustment on the converter unit also has passed through the cooling device.